The plaque was put up in 1953, but taken down about 20 years ago
A Welsh society in America wants a plaque reinstated marking the supposed arrival of a prince in the US three centuries before Columbus.
Some claim Prince Madoc ap Owain was one of the first Europeans on North American soil when he landed at Mobile Bay, Alabama, in around 1170.
A plaque marking the legend that Welsh was passed on to native Americans went up in the 50s but has now been removed.
The Alabama Welsh Society has begun a petition calling for it to be restored.
The Madoc (or Madog) legend claims he and his followers were the first Welsh emigrants to the New World when they sailed from what is now Rhos-on-Sea, Colwyn Bay.
The prince and his brother were said to be escaping the turmoil of 12th Century Wales following the death of their father, King Owain of Gwynedd.
The legend has it their two ships dropped anchor at what is now Mobile Bay, Alabama, in 1169 or 1170.
Madoc is said to have returned to Wales when up to 10 ships are claimed to have gathered at Lundy Island in the Bristol Channel before heading west.
They were never seen or heard from again but the Madoc myth continued amid claims the settlers integrated with the Mandan tribe of native Americans, who were said to have spoken a form of Welsh.
The Madoc legend was taken up by a local chapter of the group Daughters of the American Revolution, who are said to have paid for the plaque to be erected at Fort Morgan, Mobile Bay, in 1953.
The plaque read: "In memory of Prince Madoc, a Welsh explorer, who landed on the shores of Mobile Bay in 1170 and left behind, with the Indians, the Welsh language".
It is thought the plaque was taken down as the site, declared a historical landmark in 1960, focuses on the US military presence from 1800 to the end of World War II.
The Madoc plaque has been put in storage and people can view it upon request but the Alabama Welsh Society wants it to be put back in place.
Vice president Billy Price said: "Prince Madoc is believed to have discovered America hundreds of years prior to Columbus.
"Mobile could and should capitalise on this, not hide it in a storage shed.
"Prince Madoc is too important to Alabama's history to have the only plaque in our state commemorating him disappear.
"Millions of Welsh Americans know of this historical event that took place in Alabama and spend their vacations in the Mobile area all because one of their own can lay claim to being the first European who really discovered America."